(v2.5.x) Fix invalid http://asciidoctor.org references

[abelsromero]

Kind of change

• [ ] Bug fix
• [x] New non-breaking feature
• [ ] New breaking feature
• [x] Documentation update
• [ ] Build improvement

Description

What is the goal of this pull request? Port of PR https://github.com/asciidoctor/asciidoctorj/pull/1196, but for branch v2.5.x. From here :point_down:, the same stuff as in the other PR. Fix invalid http://asciidoctor.org references found in docs and JavaDocs.

How does it achieve that?

• Applied https where applicable
• Updated JavaDoc references to current links in https://docs.asciidoctor.org/

Are there any alternative ways to implement this?

No.

Are there any implications of this pull request? Anything a user must know?

No.

Issue

Fixes #1195

Release notes

Please add a corresponding entry to the file CHANGELOG.adoc

[robertpanzer]

Thanks!